Field of the Invention
The invention relates to a device and a method for cooling a reactor pressure vessel of a boiling water reactor plant.
A concept for a modern boiling water reactor plant is described, for example, in the Siemens article SWR 1000 titled “Der Siedewasser-Reaktor der Zukunft” [“The Boiling Water Reactor Of The Future”], published in the Siemens Power Journal February 1996, pages 18-22. The boiling water reactor concept described in this is distinguished, in particular, by its passive safety configurations. The reactor pressure vessel is disposed within a safety container that has, inter alia, a flood pool, from which a flood line issues into the reactor pressure vessel. In an emergency, cooling water is introduced through the flood line from the flood pool into the reactor pressure vessel solely by force of gravity. Should this “internal cooling” of the reactor pressure vessel fail, it is alternatively flooded from the outside and consequently cooled. The “external cooling” is to be triggered passively in the event of a lower filling level than the internal flooding (critical filling level).
During operation, the reactor pressure vessel of the boiling water reactor is filled with water up to a normal filling level. Above the normal filling level, a steam space follows. An important criterion for ensuring reliable operation, in particular for ensuring a sufficient cooling of the reactor, is the filling level. If this undershoots a critical filling level, the introduction of a special cooling measure takes place. To monitor the filling level, a riser pipe running parallel to the reactor is conventionally provided, which is connected in a communicating manner to the interior of the reactor pressure vessel, so that a filling level corresponding to the filling level in the reactor pressure vessel is established in the riser pipe. The actual filling level in the reactor pressure vessel is determined via a pressure measurement in the riser pipe. Such configurations for determining the filling level may be gathered, for example, from U.S. Pat. No. 5,475,720 or from U.S. Pat. No. 4,716,014. In these systems, however, there is the risk that noncondensable gases that may seriously falsify the measurement result will accumulate in the pipeline system of the riser pipe. A concept for eliminating the disturbing influences of the noncondensable gases is described in European Patent EP 0 766 813 B1, corresponding to U.S. Pat. No. 5,754,609. The known systems for measuring the filling level therefore require a very high outlay in a disadvantageous way.